02 3500 qc 6 speed dana 80.The factory detail sheet for my truck says my dana 80 is 3.55. In 5th gear truck maxes out at the tach redline just above 70 mph. I havent yet tried max top speed in 6th gear.Question for you guys running a 6 speed with 4.11's. What is your top speed in 5th gear? I'm actually curious if previous owners may have swapped in 4.11 gears on my axle. I've never driven both ratios side by side so I'm curious to know the actual difference.Or how about anyone running a confirmed 3.55? Tops speed in 5th?For one thing it's amazing to me that I can putz around town doing 35mph in 5th gear no problem without lugging/shuddering.Thanks

My 2500 with 3:55's at 70 om 6th is turning right at 2k. In 5th about 2200 at 55 I think. Never red lined it to see where it would be. Around town I usually hit 5th around 35 or 40 and can cruise around in 5th no problem. Sorry I dont have 4:10's but it sounds like you have 3:55's to me.

That sounds about right for 3.55's since I run about the same speed in 4th on my NV4500 where the tach goes red. 5th gear on the nv5600 and 4th gear on the nv4500 are both a 1.00 ratio. I also cruise around in town at 35mph in 4th gear no problem.

Thanks for the info guys.Appreciate the comparison. Sounds like I'm 3.55 after all. I'm liking the gear spread, seems like there is a good choice for everything except that I won't be going much above 70 mph when towing (I guess I shouldn't be going that fast when towing anyway! (and I will never use 6th for towing)).Regardless, I'd sure like to test drive a 6 speed with 4.11's just to see the difference!On a similar note, my first gen cummins w250 has a 5 speed getrag. I think 4th gear is 1.0 ratio? Regardless, I cannot drive around town /35 mph in 4th on that truck. Lugging big time.thanks

I have 4.10s and hate 'em...even with the automatic..

I usually tow in 6th on the interstates and similar highways around 65 to 70 in 6th. I pull a 5th wheel at 15k. I try and keep the throttle to a max of 50%. I have been doing that since it was new without any issues. Now some of the hill country I end up in wont let me do that, but for the most part I always use 6th gear. 65 if 5th is nerve racking turning all that rpm. Thats just me I guess.

I usually tow in 6th on the interstates and similar highways around 65 to 70 in 6th. I pull a 5th wheel at 15k. I try and keep the throttle to a max of 50%. I have been doing that since it was new without any issues. Now some of the hill country I end up in wont let me do that, but for the most part I always use 6th gear. 65 if 5th is nerve racking turning all that rpm. Thats just me I guess.

I read somewhere on the cummins forum that the frequent NV5600 failure issues are often due to towing in 6th gear. Something about 6th gear goes through a weak intermediary gear, weak needle bearings and the intermediary gear heating up especially under load / eg towing. Flys apart and the pieces wreck the trans. Apparently issue is compounded by the fact that the nv6500 has coooling issues/runs hot to begin with. Have a read here. It's a really long but very good thread: http://www.cumminsforum.com/forum/98-5-02-powertrain/41978-nv5600-fso6406a-6-speed-fuller.html

- - - Updated - - -

Here is another very good thread. Checkout post # 65 from Irishpowermad. http://www.cumminsforum.com/forum/98-5-02-powertrain/273121-nv5600-oil-question-6.html

I read somewhere on the cummins forum that the frequent NV5600 failure issues are often due to towing in 6th gear. Something about 6th gear goes through a weak intermediary gear, weak needle bearings and the intermediary gear heating up especially under load / eg towing. Flys apart and the pieces wreck the trans. Apparently issue is compounded by the fact that the nv6500 has coooling issues/runs hot to begin with. Have a read here. It's a really long but very good thread: http://www.cumminsforum.com/forum/98-5-02-powertrain/41978-nv5600-fso6406a-6-speed-fuller.html

- - - Updated - - -

Here is another very good thread. Checkout post # 65 from Irishpowermad. http://www.cumminsforum.com/forum/98-5-02-powertrain/273121-nv5600-oil-question-6.html

I have read a good bit of that thread before. In the very first post he says all he hauls is a 40' goose neck trailer with a case loader and all together they weigh 25k pounds. Now add about 8k for the truck and what ever he carries and he is 10k to 13k overweight depending on his rear end gearing. Now if he has alot of performance mods thats just that much more torque he is pushing thru the driveline and something is going to give. Even with regular service, thats pretty abusive. He even stated the tranny was alomost full but the fluid was burnt black.

Now I am running about 3k overweight myself. Cruising level ground in 6th I am only using 12% to 15% throttle to hold speed. On a 2% grade I can still accelerate with out using full throttle. I try and keep it 50% or less and down shift if I need more up a grade. The only time I did not use it was when it was new. And that was because the truck would not pull me up any kind of grade until the engine broke in.

I am on my second 5600. The first one got stuck in 4th gear and when I finally jerked it out it would not go back in. I also had trouble with it jumping out of 1st and reverse and occasionally 6th. I did a poor job of servicing the tranny and have to take the blame for that. That happened around 253k. The second one came from a wrecking yard with 52k according to them. I have put another 5ok on it and it is working fine so far. So I will keep using 6th for towing and I am taking better care of this one.

If I ever scattered my rear end and had to sink money into a gear set I would change front and rear to a 3.73. I've currently got 3.55s, my former 00 had 4.10s and I feel they are extreme opposites. The 4.10s are necessary for the guys that run around at or close to max gcwr most of the time, but the 3.55s are just too tall for my liking. JR

Why not jack up rear end, mark drive shaft then rotate tire. count rotations of tire and drive shaft that will give you the axle ratio.

If I ever scattered my rear end and had to sink money into a gear set I would change front and rear to a 3.73. I've currently got 3.55s, my former 00 had 4.10s and I feel they are extreme opposites. The 4.10s are necessary for the guys that run around at or close to max gcwr most of the time, but the 3.55s are just too tall for my liking. JR

I actually had 3.90 gears in my 95 1500 with a 360 and I thought those were the best of all. Had 3.55 in my 99 v10 and 02 cummins and always wanted lower, have 3.73 in my 05 and still wish I had lower like 3.90.

I tow in 6th, and I am pretty sure my motor is putting out 950-1000 ft/lbs at the crank. AFIK there are no real confirmed issues towing with a NV5600 in 6th, with the exception of (possibly) the early release smaller input shaft models. What size tires do you have? Math will tell the answer for sure. I have 3.73's and want 4.10's in every gear but 5th.